Conventionally, plasticizers are often added in order to facilitate the mixing and dispersion of materials that form a polymer composition, to enhance molding processability, or to impart performances such as flexibility to molded articles obtained from the polymer composition. Such plasticizers are required, for example, to have excellent plasticizing efficiency, to be highly compatible with resins, to show no migration, and to exhibit outstanding heat stability and light stability. Unfortunately, the fact is that the existing plasticizers do not satisfy all these performances. When a layer including such a polymer composition is used to form a laminate with a layer including another thermoplastic polymer, a high migration leads to a contamination of the other thermoplastic polymer layer and sometimes results in adverse effects such as a separation of the plasticizer-containing polymer composition layer from the thermoplastic polymer composition layer. For example, polymer compositions including a vinyl chloride-based polymer and a plasticizer (generally called soft vinyl chloride-based polymers) are materials which are used in a wide range of applications such as building materials, automobile materials, and electric and electronic materials because of their excellent properties such as flexibility, low price and workability. The use of a plasticizer in soft vinyl chloride-based polymers is indispensable in view of the fact that their excellent properties such as flexibility and workability are attributed to the presence of a plasticizer.
In light of the above aspects, it has been demanded that when a layer that includes a plasticizer-containing polymer composition is laminated together with a layer of another thermoplastic polymer composition, the plasticizer show a low tendency to migrate into the thermoplastic polymer composition layer. For example, techniques are studied in which a specific saponified ethylene-vinyl acetate copolymer is laminated on at least one side of a sheet or film which includes polyvinyl chloride containing a plasticizer (see, for example, Patent Literature 1). Further, studies are made on laminates obtained by uniting an acrylic resin layer and a vinyl chloride-based resin layer containing a specific plasticizer (for example, Patent Literature 2). Further, studies are conducted on laminates obtained by uniting a layer that includes a composition including a methacrylic resin obtained by copolymerization involving a specific UV-absorbing monomer, to an article of a polyvinyl chloride-based resin composition containing a plasticizer (for example, Patent Literature 3).
However, the fact is that when a layer including a plasticizer-containing polymer composition is united together with a layer including an acrylic thermoplastic polymer to form a laminate, the migration of the plasticizer cannot be suppressed sufficiently.
Adhesive products such as adhesive sheets, adhesive films and adhesive tapes have been used in various applications. Adhesives including an acrylic polymer have been traditionally studied for use as the adhesives in adhesive layers of these adhesive products.
Polymers are used as adherends to which such adhesives are adhered. Of such polymers, vinyl chloride-based polymers, in particular, soft vinyl chloride-based polymers have excellent workability and mechanical characteristics, and are studied for use as adherends in a wide range of applications such as building materials, automobile materials, and electric and electronic materials. Vinyl chloride-based polymers, in particular, soft vinyl chloride-based polymers generally contain a migrating component, for example, a plasticizer. The use of a plasticizer in vinyl chloride-based polymers, in particular, soft vinyl chloride-based polymers is indispensable in view of the fact that their excellent properties such as workability are attributed to the presence of a plasticizer.
When an adhesive layer is formed on an adherend which includes a vinyl chloride-based polymer containing such a migrating component, the migrating component present in the adherend migrates into the adhesive layer, sometimes causing adverse effects such as a decrease in cohesive force and a consequent separation.
In light of these aspects, it has been demanded that a migrating component, for example, a plasticizer show a reduced tendency to migrate into an adherend.
Studies are conducted on pressure-sensitive adhesive tapes or sheets which include a vinyl chloride-based polymer containing a specific plasticizer, and a pressure-sensitive adhesive layer (see, for example, Patent Literature 4). Further, techniques are studied in which a primer layer is provided between a sheet made of a vinyl chloride-based polymer and a pressure-sensitive adhesive sheet (see, for example, Patent Literatures 5 and 6). Further, adhesive compositions which include an acrylic copolymer obtained by polymerizing monomer components including an epoxy-containing specific (meth)acrylate are studied for use as pressure-sensitive adhesives for vinyl chloride-based polymer products (see, for example, Patent Literature 7).